With 70 percent of the precincts reporting, Roberts held a 48 percent to 41 percent advantage over Wolf, a radiologist and distant cousin of President Barack Obama who had argued that the incumbent wasn't conservative enough. Two other primary candidates combined for 11 percent of the vote.

The Associated Press called the race for Roberts.

The Senate's establishment is on a roll, with incumbents prevailing in Texas, Kentucky, South Carolina and Mississippi, though it took six-term Sen. Thad Cochran two tries before defeating Chris McDaniel, who is challenging the outcome.

Add Kansas to the list.

The GOP establishment blames the tea party for costing it Senate control in 2010 and 2012 as outside candidates stumbled in the general election. Republicans need to net six seats to regain the Senate, and the party has taken no chances this election cycle, putting its full force behind incumbents and mainstream candidates.

Bentivolio, a part-time reindeer rancher, was often described as the "accidental" congressman, as he was elected in 2012 when former Rep. Thaddeus McCotter turned in fraudulent voter signatures for a ballot spot. Bentivolio is the third House incumbent to lose in the primary, joining Republican Reps. Eric Cantor of Virginia, the former majority leader, and Ralph Hall of Texas on the House casualty list.

He was unapologetic in defeat.

"This is only the beginning battle to take back our country and take back our party from crony capitalists," Bentivolio said in arguing that the status quo will have to change.

"I've seen behind the curtain and I know that the ideas of Ted Cruz and Rand Paul are winning," he added.

In Kansas, Republican two-term Rep. Tim Huelskamp, who has frustrated GOP leadership and his rural constituents over his votes against the farm bill, was locked in a close race with Alan LaPolice, a farmer and educator. Huelskamp held a 53 percent to 47 percent lead with 59 percent of precincts reporting.

The four-state primary day launched a crowded stretch with Tennessee on Thursday, Hawaii on Saturday and Connecticut, Minnesota and Wisconsin next week. By month's end, voters will decide the Republican Senate nominee in a competitive race against Sen. Mark Begich in Alaska and the Democratic primary between Hawaii Sen. Brian Schatz and Rep. Colleen Hanabusa.

So far this year, the Senate's establishment is on a roll, with incumbents already prevailing in Texas, Kentucky, South Carolina and Mississippi, though it took six-term Sen. Thad Cochran two tries before defeating Chris McDaniel, who is challenging the outcome.

The 78-year-old Roberts, a conservative, moved even farther right as he faced a tough re-election. The senator, who backed the nomination of former Gov. Kathleen Sebelius to be secretary of Health and Human Services, was one of the first to call for her resignation after the disastrous launch of the health care website last October. Roberts also voted against a U.N. treaty on the rights of the disabled in December 2012 despite the appeals of former Kansas Sen. Bob Dole, who sat in a wheelchair in the well of the Senate.

Wolf argued that Roberts has spent too much time in Washington, owning a home in the nation's capital while merely renting in Kansas. Roberts didn't help his cause when he told a radio interviewer last month: "Every time I get an opponent — uh, I mean, every time I get a chance — I'm home."

In an interview on Topeka radio's WIBW NewsNow at Noon on Monday, Roberts said it was the "the height of absurdity" for people who want to replace him in Washington to criticize him for spending too much time there.

"You've got to go where the fight is," he said. "I have to work in Washington."

Wolf eagerly disavowed the policies of his cousin Obama and cast himself as a pure conservative. He had the backing of the Senate Conservatives Fund and several tea party groups.

But Wolf was dogged by X-rays of gunshot victims that he posted on a Facebook page with humorous comments. Wolf acknowledged the mistake and apologized, but Roberts made an issue in campaign ads.

"Character counts, and in my primary race, we have tried to emphasize that in terms of facts about my opponent," Roberts said this week.

In one of the fiercest House GOP primaries, two-term Kansas Rep. Mike Pompeo defeated Todd Tiahrt, who served eight terms in the House and was trying to return to Washington.

Two primaries in Michigan marked a turnabout from several years of widely heralded contests in which right-flank candidates have tried — sometimes successfully — to unseat Republican incumbents they perceive as not being conservative enough.

Bentivolio did not survive, but two-term Rep. Justin Amash did. In the 3rd Congressional District in the southwest part of the state, Amash, who has challenged the GOP leadership, defeated Brian Ellis, a 53-year-old Grand Rapids businessman who owns an investment advisory firm and serves on the school board.

Amash is popular among libertarians for his challenges to the National Security Agency's surveillance of Americans.

Five of Missouri's eight House members easily dispatched their underfunded challengers.

In Washington state, voters considered 12 candidates vying to replace 10-term Rep. Doc Hastings, a Republican who is retiring. The two candidates who collect the most mail-in ballots advance to the general election, setting up what could be a Republican-versus-Republican contest in the heavily GOP district in central Washington.